Vacuum unloading valve for dust collectors

ABSTRACT

A vacuum unloading valve for dust collectors operating under negative pressure includes a hollow elongated metal valve body having a rectangular upper inlet end for direct attachment to the depending rectangular outlet end of the collector and an elongated elastomeric sleeve surrounding and supported internally by the body throughout the greater portion of its length. The valve body includes two pairs of opposite sides, each side of one pair being of horizontally elongated, rectangular outline and each side of the other pair being elongated vertically below each side of the one pair by opposite longitudinal edges converging downwardly along convex, then concave and finally convex exponential curves symmetrical about the central longitudinal axis of each side of the other pair and merging at their lower ends in a vertical plane common to such axes. The valve sleeve includes two normally flat sheets extending around the one pair of sides onto the other pair and fitting tightly around the upper end of the valve body and loosely around the lower ends of the aforesaid edges to provide two pairs of side flaps joined at their outer margins along such axial plane but diverging downwardly from the other pair of sides and connected between such other sides by central flaps and below such edges by lower flaps. The valve also includes bars clamping the upper margins of the sleeve on the body, tying the outer margins of the side flaps together and reinforcing the central flaps, and hinge arms controlling the opening and closing of the valve sleeve which operates automatically in response to the negative operating pressure and weight of material collected.

United States Patent l72| Inventors IogerSJlrookman East Aurora; John I". Phlllippl, Tonnwanda, both of, NY. I21] Appl. No. 6,108 [22] Filed Jan. 27, I970 [45] Patented July 27, 1971 l 73] Assignee American Precision Industries, Inc.

Buffalo, N.Y.

[54] VACUUM UNLOADING VALVE FOR DUST COLLECTORS 17 China, 9 Drawing Figs.

[52] U.S.Cl 137/519, 55/432, 137/5251 [Sl] Int.Cl ..I-l6kl5/l4 [50} Fieldolsearch 55/432,

Primary Examiner-Robert G. Nilson Attomey-Sommer, Weber & Gasfel ABSTRACT: A vacuum unloading valve for dust collectors operating under negative pressure includes a hollow elongated metal valve body having a rectangular upper inlet end for direct attachment to the depending rectangular outlet end of the collector and an elongated elastomeric sleeve surrounding and supported internally by the body throughout the greater portion of its length. The valve body includes two pairs of opposite sides, each side of one pair being of horizontally elongated, rectangular outline and each side of the other pair being elongated vertically below each side of the one pair by opposite longitudinal edges converging downwardly along convex, then concave and finally convex exponential curves symmetrical about the central longitudinal axis of each side of the other pair and merging at their lower ends in a vertical plane common to such axes. The valve sleeve includes two normally flat sheets extending around the one pair of sides onto the other pair and fitting tightly around the upper end of the valve body and loosely around the lower ends of the aforesaid edges to provide two pairs of side flaps joined at their outer margins along such axial plane but diverging downwardly from the other pair of sides and connected between such other sides by central flaps and below such edges by lower flaps. The valve also includes bars clamping the upper margins of the sleeve on the body, tying the outer margins of the side flaps together and reinforcing the central flaps, and hinge arms controlling the opening and closing of the valve sleeve which operates automatically in response to the negative operating pressure and weight of material collected.

VACUUM UNLOADING VALVE FOR DUST COLLECTORS BACKGROUN D OF TH E INV ENTlON l. Field of the lnvention This invention relates to improvements in dust collectors, and more particularly to a new and improved vacuum unloading valve for a dust collector operating under negative pressure.

2. Description of the Prior Art In operating dust collectors it is necessary to dispose of the collected particulate material, and a variety of unloading valves have been designed for this purpose. One of the more recent types operates on a simple vacuum principle, the seal being maintained by negative pressure within the valve which collapses a specially formed flexible sleeve to provide an airtight seal for the discharge or outlet ends of hoppers or bins, cyclones, or any type of dust collector operating under negative pressure. The weight of the collected material forces it through the sleeve at a constant rate of flow. This vacuumtype valve has found wide acceptance as a replacement for mechanical-type seals because it functions automatically to provide an absolute seal.

Essentially, this vacuum unloading valve includes a hollow inverted conical metal valve housing or body having an outstanding upper annular flange adapted to be attached to a depending annular discharge or outlet end of a dust collector, and a hollow elongated valve sleeve molded into the wellknown "raspberry" shape from two elastomeric sheets bonded together along their side margins to provide an enlarged inverted conical upper end portion fitting over a lower inverted conical or funnel portion of the valve body. The greater portion of the length of the valve sleeve depends below the valve body without any internal support and tapers straight downwardly to a wide flat lower end which is normally closed. During operation of the dust collector under vacuum, the lower end of the valve sleeve is held closed by the pressure differential until overcome by the weight of the collected material in the valve, which forces it downwardly through the sleeve at a constant rate of flow. ln order to prevent the straight tapering opposite outer sides of the sleeve from collapsing and interfering with the desired constant flow of the collected material from the valve, these outer sides of the sleeves are provided with upwardly open pockets or scabbards receiving the lower ends of elongated leaf springs which are fulcrummed over the lower conical portion of the valve body above the valve sleeve. These springs are provided with outwardly offset upper ends which are adjustably mounted on the valve body above the sleeve to vary the force exerted by the lower ends of the springs biasing these outer sides of the sleeves apart.

However, this type of valve does have certain limitations. First, many dust collections are provided with rectangular depending discharge openings requiring the tise of an adapter element between the valve and collector, which adds to the cost of installation. Second, the molding of the valve sleeve and pockets for reception of the leaf springs not only increases manufacturing costs, but also limits the range of sizes of the valve. Third, the inverted conical shape of the valve body not only limits the capacity of the valve for any given size, but also its straight taper inherently produces a constantly increasing rate of cross-sectional area reduction per unit of descent toward the lower discharge end of the valve body, and this provides the material collected in the valve with a greater opportunity to become compacted, as in a funnel, and to form an obstruction or bridge across the mouth of the valve body, thereby interfering with and ultimately stopping the desired continuous discharge through the valve sleeve. Fourth, even though the leaf springs are effective in preventing complete collapse of the tapered sidewalls, they will yield under highvacuum conditions.

SUMMARY or THE INVENTION Accordingly, it is a primary object of the present invention to provide a new and improved vacuum unloading valve which is so constructed and designed as to overcome the various limitations of the vacuum valves referred to above. To this end, the inventive valve includes an elongated hollow valve body and an elongated elastomeric sleeve surrounding and supported internally by the valve body throughout the greater portion of its length. The valve body includes two pairs of opposite sides forming a rectangular upper inlet end mating with and adapted to be secured directly to a rectangular depending outlet end of a dust collector, as well as to increase the valve capacity for any given size, with each side of one pair being horizontally elongated and each side of the other pair being vertically elongated below those of the one pair by opposite longitudinal edges converging downwardly along lines symmetrical about the central longitudinal axis of each side of the other pair and merging at their lower ends in a vertical plane common to such axes. The valve sleeve includes two normally flat sheets which extend over the one pair of sides onto the other pair and fit tightly around the upper inlet end of the body and loosely around the lower ends of the opposite longitudinal edges to provide two pairs of side flaps which are joined at their outer margins along the axial plane but diverge downwardly from the other pair of sides and are connected by central flaps between such edges and lower flaps below the lower ends of such edges, thereby avoiding molding of the valve sleeve, and permitting construction of the valve in any range of sizes. The central flaps and side flaps normally bulge outwardly around the lower ends of such longitudinal edges to open the lower flaps, but are adapted to be drawn inwardly along these edges by the negative pressure created during operation of the dust collector to seal the lower flaps along such axial plane, as well as to be spread apart from such edges by the weight of the collected material in the valve to open the lower flaps and unload the valve, thereby producing the desired automatic operation and constant flow rate through the valve.

Another object is to provide such a valve wherein each edge on each side of the other pair includes a concave curve lying between and including exponential and hyperbolic curves tan gent to one of two straight lines tapering downwardly from the upper ends of such edges intersecting in such vertical plane above the lower ends of such edges at a predetermined common point intermediate the upper and lower ends of such one straight line and lying in a generally horizontal plane, in order to produce a substantially constant and/or decreasing rate of cross-sectional area contraction per unit of descent along such concave curve between such points of tangency and intersection, and thereby effectively prevent "bridging of the collected material across the valve body between these points while the valve is closed, as well as possible interference with opening of the valve or plugging of the discharge opening when the valve is opened.

Another object is to provide such a valve including means mounting the valve sleeve on the body and so constructed and designed as to seal the upper margins of the valve sleeve against the valve body.

Another object is to provide such a valve including means tying each pair of side flaps of the valve sleeve together and so constructed and designed as to stiffen and seal the outer margins of such side flaps.

Another object is to provide such a valve including means reinforcing the valve sleeve between the vertically elongated pair of sides and so constructed and designed as to prevent the central flaps of the valve sleeves from collapsing under high negative pressure.

Another object is to provide means controlling the opening and closing of the valve sleeves and so constructed and designed as to stabilize the opening and closing movements of the lower flaps of such valve sleeve and thereby preventing distortion and collapse of such central flaps under even higher negative pressure.

These and other objects and advantages of the invention will become apparent upon consideration of the following detailed description and accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational perspective view of a vacuum unloading valve constituting a preferred embodiment of the invention, with the valve being shown in the closed position and attached directly to a rectangular depending outlet end of a dust collector represented by broken lines;

FIG. 2 is a perspective view similar to FIG. I, but with the valve sleeve and dust collector removed to show the construction of the underlying valve body, particularly the pair of horizontally elongated sides and the pair of vertically elongated sides provided with exponentially curved edges shown in solid lines or hyperbolically curved edges shown in dotted lines;

FIG. 3 is an enlarged partial vertical sectional view taken on line 3-3 of FIG. 1, with only the left-hand portion of the front central flap of the valve sleeve, reinforcing bars thereon, and adjacent hinge structure completely broken away to show internal valve structure, and illustrating the side flaps, tie bars thereon and lower flaps of the valve sleeve in closed position in solid lines and in open position in broken lines;

FIG. 4 is an enlarged vertical sectional view taken on line 4-4 of FIG. I, and showing the central flaps and lower flaps of the valve sleeve in closed position in solid lines and in open position in broken lines;

FIG. 5 is a horizontal sectional view taken on line 5-5 of FIG. 3 and showing how the upper margins of the valve sleeve are mounted around the rectangular upper inlet end of the valve body;

FIG. 6 is an enlarged horizontal sectional view taken along line 6-6 of FIG. I and showing the valve sleeve and pairs of hinges thereon in closed position in solid lines and in open position in broken lines;

FIG. 7 is an enlarged view of the circled portion of FIG. 3 and illustrating details of the structure mounting an upper margin of the valve sleeve on a vertically elongated side of the valve body;

FIG. 8 is an enlarged view of the circled portion of FIG. 4 and illustrating details of the structure mounting an upper margin of the valve sleeve on one horizontally elongated side of the valve body, and

FIG. 9 is an enlarged view of the circled portion of FIG. 6 and illustrating details of the structure mounting one pair of hinges on the tie bars on the side flaps and on the reinforcing bars on the central flaps of the valve sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, wherein like numeral indicate like parts, and particularly FIG. I, only the depending horizontally elongated rectangular outlet end 10 of a dust collector operating under negative pressure is shown in broken lines, such outlet end being provided with two opposite pairs of outstanding perforated lower flanges 12, I4 for attachment to the vacuum unloading valve l6 which constitutes a preferred embodiment of the invention. This valve includes a hollow elongated valve body 18 (FIG. 2) and an elongated elastomeric valve sleeve 20 surrounding and supported internally by body I8 throughout the greater portion of its length. Valve body 18 is made of suitable metal, such as steel, as are the other metal parts of the inventive valve, while the sleeve is made of suitable elastomeric material such as neoprene rubber.

As best shown in FIG. 2, valve body 18 is composed of two pairs of opposite, vertically disposed sides, 22, 24 which are suitably secured together, such as by welding, to form a horizontally elongated rectangular upper inlet end mating with and adapted to be secured directly to the depending horizontally elongated rectangular outlet end 10 of the dust collector, thereby avoiding the use of an adapter and providing increased capacity over an inverted conical valve body for any given size. This direct attachment is accomplished by means of outstanding perforated upper flanges 26, 28 formed on sides 22, 24 respectively and secured in any suitable manner to flanges l2, l4 respectively of the outlet end, such as by bolts and nuts (not shown). Each of the horizontally shorter sides 22 is of horizontally elongated rectangular outline, while each of the horizontally longer sides 24 is vertically elongated below each side 22 by opposite longitudinal edges 30 converging downwardly along preferably exponentially curved lines symmetrical about the central longitudinal axis X-X of each side 24 and merging at their lower ends in a vertical plane P common to such axes.

In the preferred embodiment shown in full lines, each edge 30 includes relatively short, upper and lower convex exponential curves 30a, 30b connected by a relatively long, intermediate concave exponential curve 30c which is tangent to one of two imaginary straight lines S at a point T intermediate its upper and lower ends and lying in a horizontal plane H. The two lines S on each side 24 taper downwardly at a predetermined slope (angle to the horizontal) from the upper ends of edges 30 and intersect in plane P at point Y above the lower ends of edges 30. Thus, these lines S represent a straight line taper which would produce a continuously increasing rate of cross-sectional area contraction per unit of descent along a valve body having such a straight taper. This rate of area contraction is an important factor in determining the flow characteristics of a valve, and may be defined as:

where .4, represents the cross-sectional area of a certain section of the valve and A, the cross-sectional area of the valve one unit distance (e.g., 1 inch) below A, As will be apparent from FIG. 2, the rate of area contraction continuously increases downwardly toward points Y from the upper ends of lines S. Thus, the resistance to flow of the collected material through the valve continuously increases in the direction of flow toward the lower discharge end of the valve, and once it reaches a value exceeding the gravity force of the material, the latter will become sufficiently compacted to form a bridge or obstruction across the mouth of the valve interrupting the desired flow. The precise cross section where this will occur depends upon the slope of the valve walls, the character and moisture content of the material being collected and the compacting pressure of such material, but can be determined experimentally with a valve body (not shown) having two inverted truncated triangular walls and two rectangular walls inclined downwardly at the predetennined slope of the edges of the triangular walls to a predetermined discharge opening. Then, the critical value of R at such cross section can be calculated from the foregoing equation.

Assuming lines S to represent the edges of such triangular walls, the points T are selected so that the rate of cross-sectional area contraction at such points is less than such critical value and edges 30 are shaped between points T and Y so that they will produce a substantially constant and/or slightly decreasing rate of area contraction, in order to ensure against undesirable interruption in the desired flow. Preferably, this is accomplished by causing each edge 30 to follow a concave exponential curve 300 downwardly from point T to point Y in order to satisfy the fundamental equation given above, where R remains constant. As one alternative, each edge could be made to follow a concave hyperbolic curve 310 (shown in broken lines) between points T and Y to satisfy such equation, but where R decreases. As another alternative, an intermediate curve (not shown) lying between curves 30c and 310 could be used to satisfy such equation, where R also decreases, but not to the same degree as in the hyperbolic curve. However, whichever of the above curves is used, its slope between points T and Y obviously is at least equal to or greater than that of lines 8 to ensure against "bridging" of the material across the valve between these points when such valve is closed.

Empirical data reveal that for collecting relatively fine and dry particulate material, commonly referred to as "dust," the slope of lines S should be between about 60 and 70 and the critical value of R should not be greater than about 0.5 and preferably less than about 0.3. For the particular embodiment shown, the slope of lines S is about 68, the value of R at points T is about 0.19, and points T are located near the midpoints of lines S.

in completing the upper and lower portions of edges 30, it is preferred that concave exponential curve 30c smoothly merge with upper and lower convex exponential curves 30a, 30b. Even though the slope of curve 30c above point T may be slightly less than that of line S and thereby produce an area contraction rate slightly greater than the value of R at point T, the latter value selected is sufficiently below the critical value so that neither the upper portion of concave curve 30c or convex curve 300 will exceed such critical value. While it is necessary to exceed this critical value of R in order to close valve 16 at the bottom below points Y, the weight of the collected material above points Y is sufficiently greater than not only the resistance to flow built up below points Y but also the negative pressure produced within the valve, to fill up the space below points Y and to force valve sleeve 20 to the open position shown in broken lines in FIG. 4. In this position, the rate of area contraction at the discharge opening (junction of the now straight downwardly tapering central flaps 36 and outwardly bowed lower flaps 38 of sleeve 20) is considerably less than the critical value, being about 0.24 at a slope of about 78 for the embodiment illustrated, in order to ensure continuous flow through the valve.

Alternatively, if concave hyperbolic curve 31c or an intermediate concave curve (not shown) is employed, it is preferred that the edges 3t be completed by upper and lower convex hyperbolic curves 3la, 31b or upper and lower convex intermediate curves (not shown) respectively. Moreover, various combinations of the exponential, hyperbolic and intermediate curves could be employed, if so desired. However, whichever curve or combination of curves is employed, the same precautions as to controlling the value of R are followed, in order to ensure against bridging'of the material across the valve between points T and Y when closed, and thereby prevent possible interference with opening of the valve or blocking of the discharge opening when the valve is open.

As is apparent from FIG. 2, a greater height or vertical distance is required for a valve body having curved edges such as 30 then for one having straight edges such as represented by lines S, and a greater height is req iired for a valve body having hyperbolically curved edges such as 31 rather than exponentially curved edges 30. Therefore, the exponentially shaped edges 30 are preferred, because they require the minimum vertical height to produce the desired result of controlling the rate of area contraction, and this is particularly important where headroom is limited.

Referring now to FIGS, 1 and 35, valve sleeve 20 is composed of two normally flat and vertically elongated sheets which are slightly wider at their upper ends and of generally inverted trapezoidal outline, except for the outer portions of their upper edges which are slightly inclined outwardly tojoin their side edges at right angles. These sheets extend over sides 22 onto sides 24 and fit tightly around the upper inlet end of valve body 18 and loosely around the lower ends of edges 20 to provide two pairs of side flaps 32. These side flaps are joined at their outer margins 34 generally along plane P, but diverge (i.e. increase in width) downwardly from sides 24, as best seen in FIGv 3, and are connected by central flaps 36 between edges 30 and lower flaps 38 below such edges.

As will be evident from FIGS. 1 and 5, each sheet making up sleeve 20 represents one central flap 36 and one lower flap 38, as well as two side flaps 32, with each side flap on one sheet constituting one of each pair of side flaps joined along their outer margins 34. The use of such normally flat sleeve forming sheets eliminates molding of the valve sleeve and permits construction of the valve in any desired range of sizes.

As shown in N65. 3, 4 and 6 in broken lines, central flaps 36 and side flaps 32 normally bulge outwardly around the lower ends of edges 30 on sides 24 to open lower flaps 38. This is the "relaxed or open shape assumed by sleeve 20 whenever the dust collector is not operating, thereby ensuring complete discharge of the collected material at the end of each operation and relief of stress on the valve sleeve between operations for longer operating life. However, when the dust collector is operating under negative pressure, valve sleeve 20 closes automatically because central flaps 36 and side flaps 32 are drawn inwardly along edges 30 of sides 24 to close lower fla s 38 generally along plane P, such as shown in solid lines in FIGS. 1, 3, 4, and 6. Valve sleeve 20 is held in this "taut or closed position until automatically opened by the weight of the particulate material collected which forces central flaps 36 and side flaps 32 to be spread apart from edges 30 and to open lower flaps 38, as indicated by the broken line showing. As long as the weight of such material is sufficient to overcome the closing force produced by the negative operating pressure of the dust collector, the material will flow through the valve at the desired constant rate.

The inventive valve 16 also includes means mounting sleeve 20 on body 18, means tying each pair of side flap outer margins 34 together, means reinforcing each center flap 36, and means controlling the opening and closing of the sleeve. The mounting means are shown in FIGS. l, 3-5 and 7, 8 and includes a shorter pair of elongated and channel-shaped clamp ing bars 40 severally extending across sides 22 and a longer pair of elongated and channel-shaped clamping bars 42 extending across sides 24. As best shown in FIGS. 7 and 8, the lower flange portions 44 of these clamping bars 40, 42 engage the upper margins of the central flaps 36 and side flaps 32 respectively around the upper inlet end of valve body l8, while their upper flange portions 46 engage sides 22 and 24 respectively above such margins. Each clamping bar 42 is provided with a central notch 50 in its lower flange portion 44 and base portion 48 in order to permit passage of the upper ends of outer margins 34 of each pair of side flaps 32. This construction eliminates any undesirable folds in outer margins 34 of side flaps 32.

The mounting means are completed by a plurality of lower outstanding hanger pins 52 and upper outstanding bolts 54 spaced around the upper inlet end of body 18. Pins 52 have their inner ends welded or otherwise secured in preformed through holes in the valve body and are arranged so that one central pin projects from each of sides 22, while two pins project from each of sides 24 on opposite sides of axes X-X. Thus, pins 52 on sides 22 extend through preformed openings in the upper margins of central flaps 36, while pins 52 on sides 24 extend through similarly preformed openings in side flaps 32, in order to support such upper margins above lower flange portions 44 of the clamping bars. Bolts 54 have their inner ends similarly secured in valve body 18 and are arranged so that a pair of bolts project outwardly from each side 22, 24 above pins 52 and the upper margins of valve sleeve 20 and extend through preformed openings in base portions 48 of clamping bars 40, 42. The outer ends of bolts 54 are provided with lockwashers 56 and nuts 58 are threaded onto the bolts in order to secure clamping bars 40, 42 against the upper margins of valve sleeve 20, to effectively seal such upper margins against valve body 18.

The means tying outer margins 34 of side flaps 32 together are shown in FIGS. l, 3, 4, 6, 7 and 9, and include a pair of elongated tie bars 60 engaging the outer sides of margins 34 of each pair of side flaps 32 substantially throughout their length below each clamping bar 42. A series of longitudinally spaced bolts 62 extending through preformed holes in outer margins 34 and bars 60, together with lockwashers 56 and nuts 58 threaded onto such bolts, secure each pair of tie bars 60 and outer margins 34 together. As a result, these outer margins are not only stiffened to provide the desired valve sleeve shape, but also are effectively sealed together for proper operation of the valve. It is to be noted from NOS. 1 and 3 in particular, that the lower ends of tie bars 60 are slightly curved inwardly and when assembled with outer margins 34, cause the lower ends of such margins to assume the same curvature, in order to avoid wrinkling of lower flaps 38 and to provide a straight line juncture along the lower edges thereof when closed.

The means reinforcing central flaps 36 are shown in FIGS. l, 3, 4 and 6, and include a series of vertically spaced and horizontally elongated reinforcing bars 64 extending across the outer sides of each central flap 36 between valve body sides 22 and the lower ends ofedges 30 of sides 24. Each reinforcing bar 64 is secured to each central flap 36 by several bolts 66 passing through preformed holes in the flap and reinforcing bar, with such bolts being held in place by the aforementioned lockwashers 56 and nuts 58 threaded thereon. Reinforcing bars 64 are spaced apart sufficiently to permit each central flap 36 to conform closely to the contour of the exponentially curved edges 30 of each side 24, when valve sleeve 20 is drawn into the closed position by the negative operating pressure of the dust collector, as best shown in FIG. 4. At the same time, the reinforcing bars 64 are of sufficient length to span the distance between sides 24 and to overly their opposite longitudinal edges 30, in order to prevent cen tral flaps 36 from collapsing between sides 24 under such negative operating pressure, even through such pressure be high. As a result, not only is the desired capacity of the valve maintained, but also the desired constant flow of the collected material through the valve.

The inventive valve structure is completed by the means controlling the opening and closing of valve sleeve 20, as best shown in FIGS. 1, 3, 4, 6 and 9. The controlling means include a pair of fixed dihedral hinge arms 68 arranged between outer margins 34 of each pair of side flaps 32 and the opposite longitudinal edges 30 of each side 24, with the hinge arms being located adjacent each lower end of edges 30. As illustrated in FIG. 6, each pair of hinge arms 68 diverge intermediate their ends away from each pair of side flaps 32, in order to provide clearance for such side flaps when spread apart, as shown in broken lines. In addition, each hinge arm is pivotally connected at its outer end to a tie bar 60 and at its inner end to the adjacent end of the lowermost reinforcing bar 64 by depending hinge pins 70 welded on the arm and extending loosely through hinge pin sockets 72 welded onto each tie bar 10 and lowermost reinforcing bar 64 respectively. The loose fit or play between hinge pins 70 and sockets 72 readily permits the slightly angular movement of tie bars 60 between the solid line position of FIG. 3 and the broken line position thereof, when opening and closing valve sleeve 20. f

The connection between hinge arms 68, tie bars 60 and lower bars 64 determines the location, size and shape of the discharge opening 0 as shown in dotted lines in FIGS. 4 and 6, and as noted above, produces a slope of about 78 for the now straightened downwardly tapering central panels 36 and a value of about 0.24 for R at such discharge opening, which value is considerably less than the critical value, to avoid any interference with the desired constant flow through the valve. Thus, as shown in FIG. 6, this hinge structure controls the opening and closing of sleeve by causing the outer ends of the arms 68 of each pair to reciprocate together toward and away from those of the other pair in directions generally parallel to plane P, while the inner ends of such arms of each pair are caused to reciprocate away from and toward each other in directions generally perpendicular to plane P, in order to stabilize the opening and closing movements, respectively of lower flaps 38. Thus, when valve sleeve 20 is opened, the outer ends of each pair of hinge arms 68, together with the pair of tie bars 60 to which they are attached, move together inwardly toward the opposite pair of hinge arms and tie bars from the solid line to the broken line position shown. At the same time, the inner ends of each pair of hinge arms 68 and the lowermost reinforcing bars 64 to which they are attached, move away from each other, from the solid line position to the broken line position. Of course, the reverse movements occur when the sleeve is closed.

As a result, distortion and collapse of central flaps 36 between sides 30 are effectively prevented, even though the negative operating pressure of the dust collector might be high enough, except for the presence of the stabilizing hinge arms 68, to pull the valve sleeve and reinforcing bars 64 to one side or the other and cause partial collapse of sleeve 20 between sides 30. The counterbalancing action of the pairs of hinge arms 68 effectively prevents this undesirable effect by ensuring that the ends of reinforcing bars 64 will be retained in overlying relationship with the opposite longitudinal edges 30 of sides 24.

In assembling valve sleeve 20 on valve body 18, it is preferred that each sheet making up the sleeve be provided with the reinforcing bars 64 and then wrapped over sides 22 and onto sides 24, with the upper margins of the assembled sleeves being hung upon pins 52 to temporarily secure sleeve 20 in place. Thereafter it is but a simple matter to install clamping bars 40, 42 over the upper margins of the sleeve, to tie the outer margins of side flaps 32 together with tie bars 60, and to complete the assembly by installation of hinge arms 68. When so assembled, valve sleeve 20 will assume the relaxed or open shape shown in broken lines in FIGS. 3, 4 and 6, until automatically drawn into the "taut" or closed position shown in solid lines by the negative operating pressure of the dust collector. Once and as long as the weight of the material collected in the valve is sufficient to overcome the closing force of the negative pressure, the valve sleeve 20 once again automatically assumes and remains in the open position of the broken line showing, to permit the desired constant flow of material through the valve.

It now is clear how the invention accomplishes its various objects, and the numerous advantages of the invention likewise are apparent. While the invention has been described and illustrated herein by reference to a single preferred embodiment, it is to be understood that various changes and modifications may be made therein by those skilled in the art without departing from the inventive concept, the scope of which is to be determined by the appended claims.

What we claim is:

l. A vacuum unloading valve for a dust collector having a rectangular depending outlet end and operating under negative pressure, wherein the improvement comprises: a hollow elongated valve body and an elongated elastomeric sleeve surrounding and supported internally by said valve body throughout the greater portion of its length; said valve body including two pairs of opposite sides forming a rectangular upper inlet end mating with and adapted to be secured directly to said outlet end, one pair of sides being horizontally elongated, and the other pair of sides being vertically elongated below said one pair by opposite longitudinal edges converging downwardly along lines symmetrical about the central longitudinal axes of said other pair and merging at their lower ends in an axial plane; and said valve sleeve including two normally flat sheets extending over said one pair of sides onto said other pair of sides and fitting tightly around said upper inlet end and loosely around said lower ends of said edges to provide two pairs of side flaps joined at their outer margins generally along said plane but diverging downwardly from said other pair of sides and connected by central flaps between said edges and lower flaps below said edges, said central flaps and side flaps normally bulging outwardly around said lower ends of said edges to open said lower flaps, but being adapted to be drawn inwardly along said edges by said negative pressure to close said lower flaps generally along said plane, as well as to be spread apart from said edges by the weight of the collected material in said valve to open said lower flaps and unload said valve.

2. The unloading valve of claim I wherein each of said edges on each side of said other pair includes a concave curve lying between and including exponential and hyperbolic curves tangent to one of two straight lines tapering downwardly from the upper ends of said edges and merging in said axial plane above the lower ends of said edges at a common predetermined point intermediate the upper and lower ends of said one straight line and lying in a transverse plane generally perpendicular to said axial plane, and including means mounting said valve sleeve on said valve body; means tying each pair of said side flaps together; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve.

3. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body, said mounting means in eluding clamping bar means engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end and securing said clamping bar means against said upper margins, to seal said upper margins against said valve body.

4. The unloading valve of claim 1 including means tying each pair of said side flaps together, said tying means including elongated tie bars engaging said outer margins of said side flaps substantially throughout their length, and means securing said tie bars and outer margins together, to stiffen and seal said outer margins.

5. The unloading valve of claim 1 including means reinforc ing said valve sleeve between said other pair of sides, said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means securing said reinforcing bars and cen tral flaps together, whereby said central flaps are prevented from collapsing between said other pairs of sides under said negative pressure.

6. The unloading valve of claim I including means controlling the opening and closing of said valve sleeve, said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms being pivotally connected at their outer and inner ends to said outer margins and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.

7. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; and means tying each pair of said side flaps together; said mounting means including one pair of elongated clamping bars extending across said one pair of sides and another pair of elongated clamping bars extending across said other pair of sides, with said clamping bars engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end, extending through and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; and said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins.

8. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; and means reinforcing said valve sleeve between said other pair of sides; said mounting means including one pair of elongated clamping bars extending across said one pair of sides and another pair of elongated clamping bars extending across said other pair of sides, with said clamping bars engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end, extending through and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; and said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means extending through and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure.

9. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated clamping bars extending across said one pair of sides and another pair of elongated clamping bars extending across said other pair of sides, with said clamping bars engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end, extending through and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms of being pivotally connected at their outer and inner ends to said outer margins and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.

it). The unloading valve of claim 1 including means tying each pair of said side flaps together; and means reinforcing said valve sleeve between said other pair of sides; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length, and means extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said op posite longitudinal edges between said one pair of sides and said lower ends of said edges, and means extending through and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure.

11. The unloading valve of claim 1 including means tying each pair of said side flaps together; and means controlling the opening and closing of said valve sleeve; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length, and means extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms being pivotally connected at their outer and inner ends to said tie bars and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.

12. The unloading valve of claim 1 including means reinforcing said valve sleeve between said other pair of sides; and

means controlling the opening and closing ofsaid valve sleeve; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means extending through and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms being pivotally connected at their outer and inner ends to said outer margins and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.

13. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; means tying each pair of said side flaps together; and means reinforcing said valve sleeve between said other pair of sides; said mounting means including one pair of elongated and channel-shaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pair of sides above said upper margins, each clamping bar of said other pair being provided with a central notch in its lower flange portion and base portion permitting passage of the upper ends of said outer margins of each pair of said side flaps, and outstanding means spaced around said upper inlet end and including a plurality of threaded fasteners extending through the base portion of each of said clamping bars and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means including a series of longitudinally spaced threaded fasteners extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer side of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of threaded fasteners extending through each of said reinforcing bars and central flaps and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure.

14. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; means tying each pair of said side marginal flaps together; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated and channel-shaped clumping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pairs of sides above said upper margins, each clamping bar of said other pair being provided with a central notch in its lower flange portion and base portion permitting passage of the upper ends of said outer margins of each pair ofsaid side flaps; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means including a series of longitudinally spaced threaded fasteners extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said tie bars and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane and said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.

[5. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated and channelshaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clarnping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pairs of sides above said upper margins, each clamping bar of said other pair being provided with a central notch in its lower flange portion and base portion permitting passage of the upper ends of said outer margins of each pair of said side flaps and outstanding means spaced around said upper inlet end and including a plurality of threaded fasteners extending through the base portion of each of said clamping bars and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer side of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of threaded fasteners extending through each of said reinforcing bars and central flaps and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said outer margins and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.

lb. The unloading valve of claim l including means tying each pair of said side flaps together; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps sub stantially throughout their length, and means including a se ries of longitudinally spaced threaded fasteners extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer side of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of threaded fasteners extending through each of said reinforcing bars and central flaps and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends away from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said tie bars and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure,

17. The unloading valve of claim I wherein each of said edges on each side of said other pair includes upper and lower convex exponential curves connected by an intermediate concave exponential curve tangent to one of two straight lines tapering downwardly from the upper ends of said edges and merging in said axial plane above the lower ends of said edges at a predetermined point intermediate the upper and lower ends of said one straight line and lying in a transverse plane generally perpendicular to said axial plane, and including means mounting said valve sleeve on said valve body; means tying each pair of said side flaps together; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated and channelshaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pairs of sides above said upper margins, each bar of said other pair being provided with a central notch in its lower flange portion and base portion to permit passage of the upper ends of said outer margins of each pair of said side flaps, and outstanding means spaced around said upper inlet end and including a plurality of hanger pins extending through and supporting said upper margins above said lower flange portions, a plurality of bolts extending through each of said base portions above said upper margins and nuts threaded thereon and securing said clamping bars against said upper margins to seal said upper margins against said valve body; said tying means including a pair of elongated tie bars engaging the outer sides of said mar gins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means including a series of longitudinally spaced bolts extending through each pair of said tic bars and outer margins and nuts threaded thereon and securing each pair of said he bars and outer margins together, to stiffen and seal said outer margins; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of bolts extending through each of said reinforcing bars and central flaps and nuts threaded thereon and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of fixed dihedral hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends away from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said tie bars and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps between said other pair of sides under said negative pressure. 

1. A vacuum unloading valve for a dust collector having a rectangular depending outlet end and operating under negative pressure, wherein the improvement comprises: a hollow elongated valve body and an elongated elastomeric sleeve surrounding and supported internally by said valve body throughout the greater portion of its length; said valve body including two pairs of opposite sides forming a rectangular upper inlet end mating with and adapted to be secured directly to said outlet end, one pair of sides being horizontally elongated, and the other pair of sides being vertically elongated below said one pair by opposite longitudinal edges converging downwardly along lines symmetrical about the central longitudinal axes of said other pair and merging at their lower ends in an axial plane; and said valve sleeve including two normally flat sheets extending over said one pair of sides onto said other pair of sides and fitting tightly around said upper inlet end and loosely around said lower ends of said edges to provide two pairs of side flaps joined at their outer margins generally along said plane but diverging downwardly from said other pair of sides and connected by central flaps between said edges and lower flaps below said edges, said central flaps and side flaps normally bulging outwardly around said lower ends of said edges to open said lower flaps, but being adapted to be drawn inwardly along said edges by said negative pressure to close said lower flaps generally along said plane, as well as to be spread apart from said edges by the weight of the collected material in said valve to open said lower flaps and unload said valve.
 2. The unloading valve of claim 1 wherein each of said edges on each side of said other pair includes a concave curve lying between and including exponential and hyperbolic curves tangent to one of two straight lines tapering downwardly from the upper ends of said edges and merging in said axial plane above the lower ends of said edges at a common predetermined point intermediate the upper and lower ends of said one straight line and lying in a transverse plane generally perpendicular to said axial plane, and including means mounting said valve sleeve on said valve body; means tying each pair of said side flaps together; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve.
 3. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body, said mounting means including clamping bar means engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end and securing said clamping bar means against said upper margins, to seal said upper margins against said valve body.
 4. The unloading valve of claim 1 including means tying each pair of said side flaps together, said tying means including elongated tie bars engaging said outer margins of said side flaps substantially throughout their length, and means securing said tie bars and outer margins together, to stiffen and seal said outer margins.
 5. The unloading valve of claim 1 including means reinforcing said valve sleeve between said other pair of sides, said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pairs of sides under said negative pressure.
 6. The unloading valve of claim 1 including means controlling the opening and closing of said valve sleeve, said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms being pivotally connected at their outer and inner ends to said outer margins and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 7. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; and means tying each pair of said side flaps together; said mounting means including one pair of elongated clamping bars extending across said one pair of sides and another pair of elongated clamping bars extending across said other pair of sides, with said clamping bars engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end, extending through and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; and said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins.
 8. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; and means reinforcing said valve sleeve between said other pair of sides; said mounting meanS including one pair of elongated clamping bars extending across said one pair of sides and another pair of elongated clamping bars extending across said other pair of sides, with said clamping bars engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end, extending through and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; and said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means extending through and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure.
 9. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated clamping bars extending across said one pair of sides and another pair of elongated clamping bars extending across said other pair of sides, with said clamping bars engaging the upper margins of said central and side flaps around said upper inlet end, and outstanding means spaced around said upper inlet end, extending through and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms of being pivotally connected at their outer and inner ends to said outer margins and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 10. The unloading valve of claim 1 including means tying each pair of said side flaps together; and means reinforcing said valve sleeve between said other pair of sides; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length, and means extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means extending through and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure.
 11. The unloading valve of claim 1 including means tying each pair of said side flaps together; and means controlling the opening and closing of said valve sleeve; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length, and means extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said controlling means including a pair of hinge arms arranged between said outer marginS of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms being pivotally connected at their outer and inner ends to said tie bars and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 12. The unloading valve of claim 1 including means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means extending through and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms being pivotally connected at their outer and inner ends to said outer margins and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 13. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; means tying each pair of said side flaps together; and means reinforcing said valve sleeve between said other pair of sides; said mounting means including one pair of elongated and channel-shaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pair of sides above said upper margins, each clamping bar of said other pair being provided with a central notch in its lower flange portion and base portion permitting passage of the upper ends of said outer margins of each pair of said side flaps, and outstanding means spaced around said upper inlet end and including a plurality of threaded fasteners extending through the base portion of each of said clamping bars and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means including a series of longitudinally spaced threaded fasteners extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said reinforcing means including a series of vertically spaced and horizoNtally elongated reinforcing bars extending across the outer side of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of threaded fasteners extending through each of said reinforcing bars and central flaps and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure.
 14. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; means tying each pair of said side marginal flaps together; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated and channel-shaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pairs of sides above said upper margins, each clamping bar of said other pair being provided with a central notch in its lower flange portion and base portion permitting passage of the upper ends of said outer margins of each pair of said side flaps; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means including a series of longitudinally spaced threaded fasteners extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said tie bars and central flaps respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane and said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 15. The unloading valve of claim 1 including means mounting said valve sleeve on said valve body; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated and channel-shaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pairs of sides above said upper margins, each clamping bar of said other pair being provided with a central notch in its lower flange portion and base portion permitting passage of the upper ends of said outer margins of each pair of said side flaps and outstanding means spaced around said upper inlet end and including a plurality of threaded fasteners extending through the base portion of each of said clamping bars and securing said clamping bars against said upper margins, to seal said upper margins against said valve body; said reinforcing means including a serIes of vertically spaced and horizontally elongated reinforcing bars extending across the outer side of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of threaded fasteners extending through each of said reinforcing bars and central flaps and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said outer margins and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 16. The unloading valve of claim 1 including means tying each pair of said side flaps together; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said tying means including a pair of elongated tie bars engaging the outer sides of said outer margins of each pair of said side flaps substantially throughout their length, and means including a series of longitudinally spaced threaded fasteners extending through and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer side of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of threaded fasteners extending through each of said reinforcing bars and central flaps and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends away from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said tie bars and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps and to prevent distortion and collapse of said central flaps between said other pair of sides under said negative pressure.
 17. The unloading valve of claim 1 wherein each of said edges on each side of said other pair includes upper and lower convex exponential curves connected by an intermediate concave exponential curve tangeNt to one of two straight lines tapering downwardly from the upper ends of said edges and merging in said axial plane above the lower ends of said edges at a predetermined point intermediate the upper and lower ends of said one straight line and lying in a transverse plane generally perpendicular to said axial plane, and including means mounting said valve sleeve on said valve body; means tying each pair of said side flaps together; means reinforcing said valve sleeve between said other pair of sides; and means controlling the opening and closing of said valve sleeve; said mounting means including one pair of elongated and channel-shaped clamping bars extending across said one pair of sides and another pair of elongated and channel-shaped clamping bars extending across said other pair of sides, with said clamping bars having their lower flange portions engaging the upper margins of said central and side flaps around said upper inlet end and their upper flange portions engaging said pairs of sides above said upper margins, each bar of said other pair being provided with a central notch in its lower flange portion and base portion to permit passage of the upper ends of said outer margins of each pair of said side flaps, and outstanding means spaced around said upper inlet end and including a plurality of hanger pins extending through and supporting said upper margins above said lower flange portions, a plurality of bolts extending through each of said base portions above said upper margins and nuts threaded thereon and securing said clamping bars against said upper margins to seal said upper margins against said valve body; said tying means including a pair of elongated tie bars engaging the outer sides of said margins of each pair of said side flaps substantially throughout their length below each clamping bar of said other pair, and means including a series of longitudinally spaced bolts extending through each pair of said tie bars and outer margins and nuts threaded thereon and securing each pair of said tie bars and outer margins together, to stiffen and seal said outer margins; said reinforcing means including a series of vertically spaced and horizontally elongated reinforcing bars extending across the outer sides of each of said central flaps and overlying said opposite longitudinal edges between said one pair of sides and said lower ends of said edges, and means including a plurality of bolts extending through each of said reinforcing bars and central flaps and nuts threaded thereon and securing said reinforcing bars and central flaps together, whereby said central flaps are prevented from collapsing between said other pair of sides under said negative pressure; and said controlling means including a pair of fixed dihedral hinge arms arranged between said outer margins of each pair of said side flaps and said opposite longitudinal edges of each side of said other pair adjacent each lower end of said edges, with said arms diverging intermediate their ends away from each pair of said side flaps to provide clearance for said side flaps when spread apart and being pivotally connected at their outer and inner ends to said tie bars and the adjacent ends of the lowermost ones of said reinforcing bars respectively, whereby said outer ends of said arms of each pair reciprocate together toward and away from those of the other pair in directions generally parallel to said plane while said inner ends of said arms of each pair reciprocate away from and toward each other in directions generally perpendicular to said plane, to stabilize the opening and closing movements respectively of said lower flaps between said other pair of sides under said negative pressure. 